Enhanced clear channel assessment

ABSTRACT

A third device stores a receive signal strength of a received response data unit transmitted by a second device after receiving a first data unit transmitted by a first device. The third device obtains a clear channel access parameter included in a header of a second data unit transmitted by the first device to the second device and detects transmission exchanges in each of a plurality of service sets to use as samples of overlapping service set activity. The third device determines a minimum transmit power to be used by the third device to send a transmission to the fourth device based on transmission exchanges between devices in a particular service set. The third device determines whether to send a transmission to the fourth device based on the clear channel access parameter and minimum transmit power.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.15/150,708, filed May 10, 2016, which in turn claims priority to U.S.Provisional Patent Application No. 62/251,858, filed Nov. 6, 2015. Theentirety of each of these applications is incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to wireless networks.

BACKGROUND

Channel sensing, sometimes referred to as clear channel assessment(CCA), is a logical function that determines the current state of use ofa wireless medium. Clear Channel Assessment is implemented in thephysical layer signal processing of a wireless device and aids incontention avoidance on the wireless medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a wireless network environment in which the clearchannel assessment techniques presented herein may be employed accordingto an example embodiment.

FIG. 2 is a timing diagram depicting the signals transmitted between thewireless devices shown in FIG. 1, according to an example embodiment.

FIG. 3 is a diagram of depicting calculations made by a wireless devicein accordance with an example embodiment.

FIG. 4 is a diagram of a wireless network environment in which thecomputations depicted in FIG. 3 may be employed, according to an exampleembodiment.

FIGS. 5A and 5B are diagrams of wireless network environmentsillustrating further applications of the computations depicted in FIG. 3may be employed, according to an example embodiment.

FIGS. 6 and 7 are high-level flow charts depicting operations performedby wireless devices according to an example embodiment.

FIG. 8 is block diagram of a wireless device configured to perform theoperations presented herein, according to an example embodiment.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

Presented herein are enhanced clear channel assessment techniques. Awireless network environment is provided that includes first and seconddevices that are part of a first service set and third and fourthdevices that are part of a second service set, and the third and fourthdevices being in sufficient proximity to the first and second devices soas to receive transmissions sent between the first and second devices.The third device stores a receive signal strength of a received responsedata unit transmitted by the second device in response to reception bythe second device of a first data unit transmitted by the first device,and obtains a clear channel access parameter included in a header of asecond data unit transmitted by the first device to the second device.The third device detects transmission exchanges in each of a pluralityof service sets for use as samples of overlapping service set activityin the wireless network environment, and determines a transmit power tobe used by the third device, with respect to a particular subset of theplurality of service sets, based on the transmission exchanges betweendevices in the particular subset of the plurality of service sets. Thethird device determines whether to send a transmission from the thirddevice to the fourth device based on a comparison of the clear channelaccess parameter with a sum of the transmit power to be used by thethird device for transmission to the fourth device and the receivesignal strength of the received response data unit.

Detailed Description

Conventional Clear Channel Assessment (CCA) techniques prevent nearbytransmissions that could occur without creating interference at theoriginal link (Spatial reuse). Conventional Clear Channel Assessmenttechniques also strive to protect the region around the transmitter. Assuch, there is a need for new Clear Channel Assessment techniques.However, recently proposed Clear Channel Assessment proposals do notdiscriminate very well in the sense that the underlying algorithmsenable both “good” parallel transmissions (i.e., transmissions thatdon't interfere with the original link) and “bad” parallel transmissions(i.e., transmissions that do interfere with the original link). Anunderlying problem of conventional and recent Clear Channel Assessmenttechniques is that these algorithms attempt to protect the transmitter,when, in fact, it is the receiver that needs protection.

As such, presented herein are simple and safe Clear Channel Assessmenttechniques that protect the receiver (RX) directly, instead ofprotecting the transmitter (TX) as a proxy for the receiver. Thetechniques presented herein, called opportunistic adaptive clear channelaccess (OACCA) techniques, enable spatial reuse near atransmitter/initiator of aRequest-to-Send/Clear-to-Send/Data/Acknowledgment (RTS/CTS/Data/Ack) (orsimilar) transmission opportunity (TXOP). The initiator advertisesCCA-related parameters in the Physical Layer Convergence Protocol (PLCP)header of the Data PLCP protocol data unit (PPDU) using data measuredfrom the CTS. A third party station (STA) can use the advertisedinformation and its own received signal strength indicator (RSSI)measurements from the CTS to know at what transmit power the third partycan use for its own transmission. Also, the maximum transmission time(TXTIME) for the third party's transmission is known from the PLCPheader of the Data PPDU. A margin can provide more/less protection tothe Data PPDU, which can be made dependent on the modulation codingscheme (MCS) indicated in the PLCP header of the Data PPDU.

Also presented herein are extensions for a fourth party to acknowledgethe third party's transmission, for RTS/CTS between the third and fourthparties, as well as extensions for simple and safe Clear ChannelAssessment enabling spatial reuse near uplink multi-user multiple-inputmultiple output (UL-MU-MIMO) and uplink orthogonal frequency divisionmultiple access (UL-OFDMA) transmissions and extensions fortransmissions without RTS/CTS or shortPpdu/Ack, broadcasts,DL-MU-MIMO/OFDMA.

The techniques presented herein provide a Clear Channel Assessment in asimple, safe, and distributed manner with no averaging and trivial stateat the STAs. The techniques presented herein do not rely on isotropicantennas and work even for omnidirectional and directional antennas withbasic extensions to beamforming/antenna switching.

Reference is first made to FIG. 1. In one example of the techniquespresented herein, there are four (4) wireless devices: device A, deviceB, device C, and device D, all generally within radio frequency (RF)proximity as shown at reference numeral 10 such that they can detecttransmissions sent between each other. Devices A and B are in the sameBasic Service Set (BSS), e.g., a first BSS indicated by horizontalhatching, while devices C and D are in a different BSS, e.g., a secondBSS indicating by crisscross hatching. Thus, FIG. 1 shows overlappingBSS's. A BSS provides the basic building-block of an 802.11 wirelessLAN. In infrastructure mode, a single access point (AP) together withall associated stations (STAs) is a BSS.

As shown in FIG. 1, device C may take either of two forms denoted C-ax(if compliant with the IEEE 802.11ax standard) or C-ac (if compliantwith the IEEE 802.11ac standard). Device A wishes to transmit a longPPDU to device B, and device C wishes to transmit to device D. DevicesA, B and C-ax are all, for example, Institute of Electrical andElectronics Engineers (IEEE) 801.11ax-enabled devices. However, thetechniques may be implemented with devices that follow another 802.11amendment, another standard, or another specification. Devices A, B,C-ax, C-ac and D are also identified by reference numerals 12(1), 12(2),12(3), 12(4) and 12(5), respectively. Each of these devices may have oneor a plurality of antennas, as denoted at reference numerals14(1)-14(5), respectively.

Reference is now made to FIG. 2. Device A contends and becomes the TXOPholder. Device A initiates a transmission sequence to device B bytransmitting to device B a first data unit 20 that is configured toprovoke a response data unit 22 by device B, followed by transmission todevice B of a second data unit 30 to which device B is to send anacknowledgment 32. For example, devices A and B perform a shortPPDU/response PPDU/long PPDU/acknowledgement sequence. The first dataunit 20 (e.g., short PPDU) may be a Request-to-Send (RTS) frame and thesecond data unit 22 (e.g., response PPDU) may be a Clear-to-Send (CTS)frame. In the middle of this TXOP, device A records the RSSI of theresponse PPDU as RSSI_BA, and device A combines the recorded RSSI(RSSI_BA) with the conducted transmit power it used for the long PPDU,referred to as TX_A, to compute a clear channel access parameterreferred to as the “simpleSafeCcaParameter.” In other words, thesimpleSafeCcaParameter (SSCP) is defined as:

-   -   simpleSafeCcaParameter=TX_A+RSSI_BA, where RSSI_BA is the RSSI        of device B's transmission received at device A.

Device A quantizes the simpleSafeCcaParameter to a several bits (e.g., 5bits at 3 dB resolution, 4 bits at 6 dB resolution, etc.) and includesthe quantized simpleSafeCcaParameter (SSCP) in the PLCP header 40 of thelong PPDU 30, sent robustly in the preamble of the transmission (e.g. inthe PLCP header in accordance with the IEEE 802.11ax PHY format).

Device C detects the presence of the response PPDU (e.g., a preambleSIFS after the short PPDU; or a MAC header in a PPDU with RA==TA offrame in PPDU starting SIFS beforehand) and records its RSSI as RSSI_BC.Device C also receives the simpleSafeCcaParameter from the PLCP headerof the long PPDU from device A.

In one embodiment, device C is permitted to transmit to device D underthe following conditions:

a. simpleSafeCcaParameter>TX_C+RSSI_BC+Margin; and

b. The C/D TXOP completes before the end of the longPpdu sent by deviceA.

For example, device C may transmit a first (short PPDU), such as an RTSframe, shown at 50, to provoke a short response PPDU (such as a CTSframe), shown at reference numeral 52, from device D. Thereafter, deviceC can transmit a longer PPDU 60 to which device D can sent anacknowledgment 62.

Device D is permitted to respond to device C under the followingcondition:

simpleSafeCcaParameter>TX_D+RSSI_BD+Margin.

In another embodiment, device C is permitted to transmit to device Dwhen the following conditions are satisfied:

a. No immediate response is solicited from device D;

b. The transmission by device C completes before the end of the longPPDU sent by device A; and

c. simpleSafeCcaParameter>TX_C+RSSI_BC+Margin.

Device C is aware of its own conducted power that it will use totransmit to device D, where this power is referred to as TX_C. Device Cmay reduce TX_C in order to comply with the above transmission conditionc) (i.e., simpleSafeCcaParameter>TX_C+RSSI_BC+Margin). This is the samefor device D. The Margin could be a fixed number, or an MCS-dependentnumber plus a fixed additional margin. The fixed margin or additionalmargin might be standardized or advertised by the AP. In a furtherembodiment, M may be included in the transmitted parameter: i.e.simpleSafeCcaParameterAlternate=simple SafeCcaParameter−Margin. Ifdevice C cannot even hear the response PPDU, then device C can use somelow RSSI at its sensitivity instead (e.g. −82 dBm).

Device B can receive a PPDU from device A even if device C transmits solong as:

TX_A+G_AB−PL_AB>TX_C+G_CB−PL_+M  (1),

where G_xy==G_yx is the antenna gain between x and y, PL_xy==PL_yx isthe pathloss between x and y and M is Margin. For now, the antenna gainis assumed to be static (i.e. no antenna switching or digitalbeamforming).

As shown above, observable at device C are thesimpleSafeCcaParameter=TX_A+RSSI_BA); TX_C; RSSI_BC (RSSI_BC is RSSI ofB's transmission heard at C); and M. Also known are:

TX_B+G_AB−PL_AB=RSSI_BA  (2)

TX_B+G_BC−PL_BC=RSSI_BC  (3)

Rearranging (2) and (3) yields:

G_AB−PL_AB=RSSI_BA−TX_B  (2a)

G_BC−PL_BC=RSSI_BC−TX_B  (3a)

Inserting (2a) and (3a) into (1) yields:

TX_A+RSSI_BA−TX_B>TX_C+RSSI BC_TX_B +M  (1a).

Cancelling −TX_B on both sides, yields:

TX_A+RSSI_BA>TX_C+RSSI_BC+M  (1b).

As noted:

simpleSafeCcaParameter=TX_A+RSSI_BA  (4)

Inserting (4) into (1b) yields:

simpleSafeCcaParameter>TX_C+RSSI_BC+M  (1c).

Therefore, equation (1c) provides a simple rule for device C where allparameters (a, b, and c) are observable at device C.

As described above in connection with FIG. 1, the devices A, B, C and Dmay have a single antenna or a plurality of antennas. A plurality ofantennas, and associated signal processing, enables a device to beamforma transmission to another device, and also enables a device to sendmultiple spatial streams simultaneously using multiple-inputmultiple-output (MIMO) wireless communication techniques. Furthermore,devices equipped with multiple antennas and associated signal processingcapability can participate in multi-user MIMO communication (MU-MIMO)techniques in which one device can simultaneously send multipletransmissions to respective ones of a plurality of destination devices.

In the above examples, device D (I) is only solicited for an Ack/BlockAck (BA) by device C if (II) device C successfully performs an RTS/CTS,(III) the antenna gain is assumed static, and device C cannot transmit(IV) when device A is soliciting an uplink-orthogonal frequency divisionmultiple access (UL-OFDMA) or uplink-multi-user MIMO (UL-MU_MIMO)transmission, (V) when device A's transmit opportunity (TXOP) does notstart with a RTS/CTS or shortPpdu/Ack, or (VI) when device A istransmitting a downlink-OFDMA/downlink MU-MIMO (DL-OFDMA/DL-MU-MIMO)transmission. The above techniques may be extended to at least partiallyaddress these issues, wherein extending the above to address theseissues, noting that issues (V) and (IV) can be solved but at higherscanning, OBSS frame parsing and storage costs at device C.

Regarding issue (II), if device D is IEEE 802.11ax-enabled, then it canperform Clear Channel Assessment in the same way as device C, anddetermine if its response frame(s) (CTS, Ack, BA, etc.) do not interferewith the reception of device A's PPDU at device B. If Clear ChannelAssessment at device D looks clear, then it can send an immediateacknowledgement before the end of device A's PPDU to device B. Theimmediate acknowledgement might be an “unsolicited BA” or, in certainexamples, a new Block Ack Response (BAR) mode (e.g., respond ifpossible, else wait for poll).

Regarding issue (III), the RSSI detected at each device will depend onwhether beamforming/no beamforming is used during each of the PPDUs. ThePPDUs carrying RTS/CTS are typically not beamformed, but the long PPDU,and potentially device C's transmission to device D, might bebeamformed. In this case, the rule evolves (math omitted) to yield:

TX_A+BF_AB,B+RSSI_BA>TX_C+BF_CB,D+RSSI_BC+M  (III-1b)

where BF_AB,B is the additional beamforming gain between device A anddevice B when device A is sending a PPDU to device B, and is greaterthan or equal to 0 dB under almost all circumstances, and BF_CB,D is theadditional beamforming gain between device C and device B when device Cis sending a PPDU to device D, and is less than or around 0 dB underalmost all circumstances.

Accordingly, presented are additional embodiments. For example, deviceA, knowing the channel state information (CSI) from device A to deviceB, may compute BF_AB,B and send:

simpleSafeCcaParameter=TX_A+BF_AB,B+RSSI_BA.

Alternatively, it is possible to leave BF_AB,B=0. Knowing the CSI fromdevice B to device C, and assuming channel reciprocity (perhaps withdevice C's TX/RX calibration), device C may use BF_CB,D in its transmitdecision as:

simpleSafeCcaParameter>TX_C+BF_CB,D+RSSI_BC+M.

In a further alternative, it may be possible to leave BF_CB,D=0. Ifeither device A or device C (or both) perform the simplified operation(i.e., make simpleSafeCcaParameter=TX_A+BF_AB,B+RSSI_BA and/or makesimpleSafeCcaParameter>TX_C+BF_CB,D+RSSI_BC+M), under the assumptionsthat BF AB,B=0 and BF CB,D<=0, from above, the effect is that device Cneeds to transmit at a lower conducted power than it might otherwise, ornot transmit at all. This implies less interference to the transmissionfrom device A to device B, so no harm is done.

Regarding issue (IV), for UL-MU-MIMO or UL-OFDMA, device A is thereceiver and the clients (device Bs) are the transmitters. Typically,there is some brief polling by device A of the device Bs (e.g., “do youhave traffic for me”) followed shortly by device A's trigger frame tosolicit transmissions from the device Bs, followed (after approximatelyan SIFS) by the uplink transmissions from the device Bs. From the bufferpolling (or PS-Poll frames or unscheduled automatic power-save delivery(UAPSD) trigger frames), device A has a good estimate of the RSSI fromeach device B to device A at device B′s nominal conducted power(RSSI_BA). In certain examples, the buffer poll frame could includedevice B′s RSSI measurement of a PPDU from device A, referred to asRSSI_BA.

Alternatively, the trigger frame is expected to specify some powercontrol (since this is required for UL-MU-MIMO or UL-OFDMA to workreasonably reliably). In this way, device A has a good idea of TX_B orRSSI_BA for all the B devices. Using similar computations as above, itis possible to show that device A should sendsimpleSafeCcaParameter=TX_A+min(TX_A−TX_B+RSSI_BA) orsimpleSafeCcaParameter=TX_A+min(RSSI_BA), if RSSI_BA is available in thePLCP header of the PPDU carrying a trigger frame, plus an indicationthat this is a trigger frame (which may be 1 new bit in the PLCP, forrange, or the existing MAC-level frame type/subtype field).

In one embodiment, device C measures RSSI_AC from the Trigger PPDU, andis permitted to transmit to device D under the following conditions:

a. simpleSafeCcaParameter>TX_C+RSSI_AC+Margin; and

b. The C/D TXOP completes before the end of the longPpdu sent by thedevice B's.

Device D is permitted to respond to device C under the followingconditions:

simpleSafeCcaParameter>TX_D+RSSI_AD+Margin.

In another embodiment, device C measures RSSI_AC from the Trigger PPDUand is permitted to transmit to device D under the following conditions:

a. No immediate response is solicited from device D, unless device Dalso performs simple safe CCA before device D's response;

b. The transmission by device C (plus any acknowledgement from device D)completes before the end of the long PPDU sent by device A; and

c. simpleSafeCcaParameter>TX_C+RSSI_AC+Margin.

Regarding issue (V), if device A's TXOP does not start with RTS/CTS or ashortPpdu/Ack, then the CCA rule can work, but more operations arerequired at device A and device C. In particular, device A needs to usea recent transmission from device C to device A to measure RSSI_BA (andmay add a safety factor dependent on age, if retried, MCS, ifbeamforming was indicated, etc.). Device C needs to scan and measure theRSSI of other clients to measure RSSI_BC (and may add a safety factordependent on age, if retried, MCS, if beamforming was indicated, etc.).If device C does not perform the scanning or does not have informationabout RSSI_BC, device C is not permitted to transmit during the longPPDU. This incentivizes device C to scan and may limit this mode ofoperation to devices with wall power or large batteries (e.g., APs,laptops).

Regarding issues (III) and (V), yet another embodiment is describedbelow. If device B is using beamforming to transmit to device A, deviceB quantizes its expected beamforming gain to a few bits and includes thequantized beamforming gain in the PLCP header of its transmitted PPDU.Using this information, device A may adjust its computation of thesimpleSafeCcaParameter as follows:

simpleSafeCcaParameter=TX_A+BF_AB,B+RSSI_BA−BF_BA,A

Furthermore, regarding issues (III) and (V), it is observed thatbeamforming gains can vary widely over time. As a result, device A canadjust the BF_AB,B and BF_BA,A values by conservatively choosing theBF_AB,B from a lower percentile of the gain's distribution over time,and choosing the BF_BA,A from a higher percentile of the gain'sdistribution.

Thus, device A may compute the simpleSafeCcaParameter based on abeamforming gain from the first device to the second device.Furthermore, the simpleSafeCcaParameter may be computed based on aminimum of a sum of a beamforming gain from the first device to thesecond device and the receive signal strength of the response data unit,over a plurality of second devices in the first basic service set.

Regarding issue (VI), a broadcast DL-OFDMA/DL-MU-MIMO transmission is anextension of (IV), where an AP sendssimpleSafeCcaParameter=TX_A+min(BF_AB,B+RSSI_BA) and the minimum (min)is over many device B recipients in the AP's BSS, and device C appliessimpleSafeCcaParameter>TX_C+max(RSSI_BC+Margin, where the max(RSSI_BC)is over all clients addressed by the broadcast or DL transmission, or(for simplicity) over all clients with the same BSS COLOR as the senderof the broadcast or DL transmission.

BSS color is indicated by a plurality of bits, e.g., 6 bits, and is usedto denote different BSS's that are operating on the same channel. EachBSS has a different color that enables clients to know whether atransmission is within their BSS or not after decoding the SIG field.Transmissions within the BSS are deferred to at the lowest possiblelevel in order to provide the lowest sensitivity and prevent intra-BSSmultiple unsynchronized transmissions. Transmissions which belong to anOBSS (different color) are deferred to using the CCA techniquespresented herein. Said another way, a BSS color is a subset of aplurality of service sets.

As an additional means for addressing OBSS interference issues, device Acan count the number of times it has discontinued decoding a PPDUreceived above the CCA level and switched to decoding another strongerPPDU, where the stronger PPDU has been an OBSS IEEE 802.11ax PPDU. Thiscount is measured over a recent time window and can be added as apenalty to the simpleSafeCcaParameter. This, in effect, acts as aquasi-closed-loop power control to reduce transmit power in theneighboring OBSS.

With reference to FIGS. 3 and 4, still another embodiment is describedas follows. Device C maintains a table with number of rows equal to thenumber of BSS_COLORs and minTX as columns, or more generally, aminimum/averaging state associated with that BSS_COLOR, e.g., minimum ofthe current window and immediately previous window, PPDU count perwindow. For each “shortPpdu+responsePpdu+high-efficiency PPDU (hePpdu)”exchange or “[Beacon or other AP frame] . . . hePpdu+responsePpdu”exchange pair (hePpdu could be PS-Poll/UAPSD trigger) sniffed by deviceC, device C:

a. Determines TX_C_permittedMax<simpleSafeCcaParameter−(RSSI_BC+M); and

b. Updates the minTX for that BSS_COLOR.

As shown in FIG. 3, device C calculates a minimum of TX_C_permittedMaxevery 110 exchanges (or 110 ms), and a minimum of TX_C_permittedMax overthe exchanges since the last whole 110 (or 110 ms slot), and thenminTXnew=min(minimum of TX_C_permittedMax every 110 exchanges/ms, aminimum of TX_C_permittedMax over the exchanges since the last whole 110exchanges/ms). The minTX tracks the minimum of TX_C_permittedMax acrossthe current partial window plus the previous full window.

The numbers in FIG. 3 are examples only, the min(.) operator may bereplaced by some min-like function that includes some level of averagingalso, and maintaining a reference over one “window” and any subsequentfractional window might be generalized too, to a sliding window,multiple windows and so forth.

In this embodiment, device C can transmit during a PPDU with a differentBSS_COLOR at TX_C if a) TX_C<=minTX for that BSS_COLOR orb) VHT CCArules permit it to do so.

As a summary, in this embodiment, it is proposed to use“shortPpdu+responsePpdu+hePpdu” or “Beacon . . . hePpdu+responsePpdu” assamples from which to learn about the OBSS environment, organized perBSS_COLOR. The proposed learning (i.e., the min operator over a recentwindow) is deliberately chosen to be highly responsive to changedconditions including new transmitters. As shown in FIG. 4, when there isa good separation between BSS's, device C will learn it can routinelyuse a relatively high TX_C.

An extension to this embodiment further addresses intermittenttransmitters. If an intermittent transmitter is far from its intendedreceiver and has not transmitted in the last 110+ exchanges/ms, then itsneighbors' minTX values do not account for the intermittent transmitter.The extension may use a) non-HE PPDU or b) RSSI from a Beacon frame,then HE PPDU+Ack/BA, or c) RTS+CTS or shortLegacyPpdu+Ack before an HEPPDU. Either b) or c) immediately updates the Simple Safe CCA rule(minTX) of their neighbors.

A further extension to this embodiment addresses Power Save devices.Upon wake-up, power save devices do not have adequate information (e.g.,they do not have data on the last 110+ exchanges/ms). The extensionrequires power save devices to use very high throughput (VHT) CCA rulesuntil they have adequate information. An alternative is for an AP topush down minTX values (e.g. 64 values*4-8 bits) in response to aPS-Poll or UAPSD trigger frame taking into account recent and historicalminTX tables. In this extension, clients may send (after a request,unsolicited, or periodically) their minTX tables to their associated AP.

Thus, device C may send, to one or more associated client devices, datafor the minimum transmit power, with respect to the particular subset ofthe plurality of service sets, or receive from one or more clientdevices, data or the minimum transmit power.

A third extension to this embodiment proposes to split information abouteach neighboring BSS color into two or more bins based on the receivedRSSI from the PPDUs originating from that BSS color. A separateTX_C_permitted max is computed for each bin. The transmitting device Cobtains its power output limit based on the BSS color of the presentpacket, as well as its RSSI such that the correct bin from this BSScolor's information can be chosen.

FIG. 5A shows an example, similar to that shown in FIG. 4. However, inFIG. 5, there is poor separation between neighboring BSSs BSS 1 and BSS2. That is, device 70, which is part of BSS 2 and is a frequenttransmitter, is quite close to device C. Device C learns that maxTX islow, in which case it will defer to transmissions for BSS 2. In FIG. 5B,by contrast, device 80, which is part of BSS 2, is an intermittenttransmitter. Even though device 80 transmits intermittently, it canimmediately refresh the maxTX of neighboring device C using RTS/CTSbefore its longPpdu.

Reference is now made to FIG. 6 for a description of a high-level flowchart depicting operations performed by a wireless device according tothe embodiments presented herein. This flow chart depicts operationsperformed by one of a plurality of wireless devices operating in awireless network. The wireless network environment includes first andsecond devices that are part of a first service set and third and fourthdevices that are part of a second service set. The third and fourthdevices are sufficiently proximate to the first and second devices so asto receive transmissions sent between the first and second devices. Instep 100, the first device initiates a transmission sequence to thesecond device by transmitting to the second device a first data unitthat is configured to provoke a response data unit, followed bytransmission to the second device of a second data unit that isconfigured to provoke an acknowledgment transmission by the seconddevice. In step 110, the first device stores a receive signal strengthof the response data unit received by the first device. At 120, thefirst device computes a clear channel access parameter based on a sum ofa transmit power used for transmitting the second data unit and thereceive signal strength of the response data unit. At 130, the firstdevice includes the clear channel access parameter in a header of thesecond data unit that is transmitted to the second device.

Reference is now made to FIG. 7. FIG. 7 illustrates operations performedby the third device in the wireless network environment described abovein connection with FIG. 6. At 200, the third device stores a receivesignal strength of the response data unit received by the third device.At 210, the third device receives the clear channel access parametercontained in the header of the second data unit (transmitted by thefirst device to the second device).

At 220, transmission exchanges are detected in each of a plurality ofservice sets for use as samples of overlapping service set activity inthe wireless network environment.

At 230, a transmit power is determined to be used by the third device,with respect to a particular subset (e.g., a particular BSS color) ofthe plurality of service sets, based on the transmission exchangesbetween devices in the particular subset of the plurality ofservicesets.

At 240, the third device determines whether to send a transmission tothe fourth device based on a comparison of the clear channel accessparameter with a sum of the transmit power to be used by the thirddevice for the transmission to the fourth device and the receive signalstrength of the response data unit received by the third device.

The determination in step 240 may involve determining to send thetransmission to the fourth device when the clear channel accessparameter is greater than a sum of the transmit power to be used by thethird device for the transmission to the fourth device and the receivesignal strength of the response data unit received by the third device.Moreover, this determining may involve comparing the clear channelaccess parameter with the sum of the transmit power to be used by thethird device for the transmission to the fourth device, the receivesignal strength of the response data unit received by the third device,and a margin value. The margin value may be a fixed value or dependenton a modulation and coding scheme used by the third device to send thetransmission to the fourth device. Further still, the margin value maybe advertised in a data unit transmitted by the first device. Furtheryet, the third device may determine to transmit during a data unittransmitted in the particular subset of the plurality of service setswhen the transmit power used by the third device is less than theminimum transmit power for the particular subset of the plurality ofservice sets.

The determination step 230 may involve computing a maximum transmitpower permitted to be used by the third device, with respect to theparticular subset of the plurality of service sets, based ontransmission exchanges between devices in the particular subset of theplurality of service sets that are received by the third device;computing a first minimum of the maximum transmit power over a timewindow spanned by a predetermined number of transmission exchanges and asecond minimum of the maximum of the transmit power since a most recenttime window; updating a minimum transmit power to be used by the thirddevice, with respect to the particular subset of the plurality ofservice sets, based on a minimum of the first minimum and the secondminimum; and storing the minimum transmit power with respect to theparticular subset of the plurality of service sets, at the third device.

The transmission exchanges that are observed/detected by the thirddevice as samples of activity in overlapping service sets may include:(a) a non-high efficiency data unit sent by the first device followed bya high-efficiency data unit sent by the first device and anacknowledgment; (b) a Beacon frame sent by the first device, followed bya high-efficiency data unit sent by the first device and anacknowledgement; (c) a request-to-send/clear-to-send exchange before ahigh efficiency data unit; or (d) a short legacy data unit followed byan acknowledgment before a high efficiency data unit.

Reference is now made to FIG. 8 for a description of a wireless devicethat may be configured to perform the operations described herein. Theblock diagram shown in FIG. 8 is representative of any of the deviceswhose operations are described above in connection with FIGS. 1-7, andmay be for an AP or a client device (STA). The wireless device includesa plurality of transmit upconverters 400(1)-400(K) each connected to acorresponding one of the antennas 405(1)-405(K) and a plurality ofreceive downconverters 410(1)-410(K) each connected to a correspondingone of the antennas 405(1)-405(K). FIG. 8 is meant to cover the case inwhich a wireless device has multiple antennas and signal processingcapabilities for MIMO and beamforming techniques, as described above.

A baseband signal processor 420 (e.g., modem) is provided that isconnected to the plurality of transmit upconverters 400(1)-400(K) and tothe plurality of receive downconverters 410(1)-410(K). The basebandsignal processor 420 performs the baseband transmit signal processing ofsignals to be transmitted via the plurality of antennas 405(1)-405(K),e.g., for MU-MIMO and single user transmissions, and performs thebaseband receive processing of signals that are received by theplurality of antennas 405(1)-405(K). The baseband signal processor 420may take the form of one or more integrated circuits including fixed orprogrammable digital logic gates to perform various functions such asanalog-to-digital conversion, digital-to-analog conversion, Fast FourierTransform, etc.

A controller 430 is provided that may take the form of one or moremicroprocessors or microcontrollers. A memory 440 is provided thatstores instructions for control software 450. There also is a networkinterface unit 460 that enables wired network connectivity.Alternatively, the controller may be embodied by one or more integratedcircuits including fixed or programmable digital logic gates.

The memory 440 may include read only memory (ROM), random access memory(RAM), magnetic disk storage media devices, optical storage mediadevices, flash memory devices, electrical, optical, or otherphysical/tangible memory storage devices. Thus, in general, the memory440 may include one or more tangible (non-transitory) computer readablestorage media (e.g., a memory device) encoded with control software 450comprising computer executable instructions and when the software isexecuted (by the controller 430) it is operable to perform theoperations described herein.

The signal processing operations described herein may be performed bythe baseband signal processor 420 alone using digital signal processingtechniques, the controller 430 alone, or partly by the baseband signalprocessor 420 and party by the controller 430. In one form, the basebandsignal processor 420 is implemented in one or more application specificintegrated circuits (ASICs).

In summary, a wireless network environment includes first and seconddevices that are part of a first service set and third and fourthdevices that are part of a second service set. The third and fourthdevices are sufficiently proximate to the first and second devices suchthat the third and fourth devices receive transmissions sent between thefirst and second devices. In such a wireless network environment, thethird device may perform a method that includes storing a receive signalstrength of a received response data unit transmitted by the seconddevice in response to reception by the second device of a first dataunit transmitted by the first device. The method further includesobtaining a clear channel access parameter included in a header of asecond data unit transmitted by the first device to the second device.Moreover, the third device may detect transmission exchanges in each ofa plurality of service sets for use as samples of overlapping serviceset activity in the wireless network environment. The method thendetermines a minimum transmit power to be used by the third device, withrespect to a particular subset of the plurality of service sets, basedon the transmission exchanges between devices in the particular subsetof the plurality of service sets. The third device may then determinewhether to send a transmission from the third device to the fourthdevice based on a comparison of the clear channel access parameter witha sum of the minimum transmit power to be used by the third device fortransmission to the fourth device and the receive signal strength of thereceived response data unit.

In another embodiment, the method determines the minimum transmit powerto be used by the third device by computing a maximum transmit powerpermitted to be used by the third device, with respect to the particularsubset of the plurality of service sets, based on transmission exchangesbetween devices in the particular subset of the plurality of servicesets; computing a first minimum of the maximum transmit power over atime window spanned by a predetermined number of transmission exchangesand a second minimum of the maximum of the transmit power since a mostrecent time window; updating the minimum transmit power to be used bythe third device, with respect to the particular subset of the pluralityof service sets, based on a minimum of the first minimum and the secondminimum; and storing the minimum transmit power with respect to theparticular subset of the plurality of service sets, at the third device.

In another aspect, the method further includes determining to transmitduring a data unit transmitted in the particular subset of the pluralityof service sets when the transmit power used by the third device is lessthan the minimum transmit power for the particular subset of theplurality of service sets.

In another embodiment, the transmission exchanges include (a) a non-highefficiency data unit sent by the first device followed by ahigh-efficiency data unit sent by the first device and anacknowledgment; (b) a Beacon frame sent by the first device, followed bya high-efficiency data unit sent by the first device and anacknowledgement; (c) a request-to-send/clear-to-send exchange before ahigh efficiency data unit; or (d) a short legacy data unit followed byan acknowledgment before a high efficiency data unit.

In yet another embodiment, the method also includes sending, to one ormore associated client devices, data for the minimum transmit power,with respect to particular subset of the plurality of service sets, orreceiving from one or more client devices, data or the minimum transmitpower.

Moreover, the clear channel access parameter is based on a sum of atransmit power used by the first device to transmit the second data unitto the second device and a receive signal strength of the response dataunit at the first device.

In another aspect, the method also includes determining to send thetransmission to the fourth device when the clear channel accessparameter is greater than a sum of the transmit power to be used by thethird device for the transmission to the fourth device and the receivesignal strength of the response data unit received by the third device.

In another embodiment, an apparatus includes a communication interfaceconfigured to enable network communications and a processing devicecoupled with the communication interface. The processing device isconfigured to store a receive signal strength of a received responsedata unit transmitted by a first device in response to reception by thefirst device of a first data unit transmitted by a second device; obtaina clear channel access parameter included in a header of a second dataunit transmitted by the second device to the first device; detecttransmission exchanges in each of a plurality of service sets for use assamples of overlapping service set activity in a wireless networkenvironment; determine a minimum transmit power to be used, with respectto a particular subset of the plurality of service sets, based on thetransmission exchanges between devices in the particular subset of theplurality of service sets; and determine whether to send a transmissionto a third device based on a comparison of the clear channel accessparameter with a sum of the minimum transmit power to be used fortransmission to the third device and the receive signal strength of thereceived response data unit.

In yet another embodiment, one or more non-transitory computer readablestorage media is encoded with instructions that, when executed by aprocessor, cause the processor to store a receive signal strength of areceived response data unit transmitted by a first device in response toreception by the first device of a first data unit transmitted by asecond device; obtain a clear channel access parameter included in aheader of a second data unit transmitted by the second device to thefirst device; detect transmission exchanges in each of a plurality ofservice sets for use as samples of overlapping service set activity in awireless network environment; determine a minimum transmit power to beused, with respect to a particular subset of the plurality of servicesets, based on the transmission exchanges between devices in theparticular subset of the plurality of service sets; and determinewhether to send a transmission to a third device based on a comparisonof the clear channel access parameter with a sum of the minimum transmitpower to be used for transmission to the third device and the receivesignal strength of the received response data unit.

The above description is intended by way of example only. The conceptsdescribed herein may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Theforegoing examples are therefore to be considered in all respectsillustrative and not meant to be limiting. Accordingly, it is intendedto embrace all such alterations, modifications and variations that fallwithin the spirit and scope of any claims filed in applications claimingpriority hereto interpreted in accordance with the breadth to which theyare fairly, legally and equitably entitled.

What is claimed is:
 1. In a wireless network environment that includesfirst and second devices that are part of a first service set and thirdand fourth devices that are part of a second service set, and the thirdand fourth devices being in sufficient proximity to the first and seconddevices to receive transmissions sent between the first and seconddevices, a method comprising: storing at the third device a receivesignal strength of a received response data unit transmitted by thesecond device in response to reception by the second device of a firstdata unit transmitted by the first device; obtaining a clear channelaccess parameter included in a header of a second data unit transmittedby the first device to the second device; detecting transmissionexchanges in each of a plurality of service sets for use as samples ofoverlapping service set activity in the wireless network environment;determining a minimum transmit power to be used by the third device,with respect to a particular subset of the plurality of service sets,based on the transmission exchanges between devices in the particularsubset of the plurality of service sets; and determining whether to senda transmission from the third device to the fourth device based on acomparison of the clear channel access parameter with a sum of theminimum transmit power to be used by the third device for transmissionto the fourth device and the receive signal strength of the receivedresponse data unit.
 2. The method of claim 1, wherein determining theminimum transmit power to be used by the third device comprises:computing a maximum transmit power permitted to be used by the thirddevice, with respect to the particular subset of the plurality ofservice sets, based on transmission exchanges between devices in theparticular subset of the plurality of service sets; computing a firstminimum of the maximum transmit power over a time window spanned by apredetermined number of transmission exchanges and a second minimum ofthe maximum of the transmit power since a most recent time window;updating the minimum transmit power to be used by the third device, withrespect to the particular subset of the plurality of service sets, basedon a minimum of the first minimum and the second minimum; and storingthe minimum transmit power with respect to the particular subset of theplurality of service sets, at the third device.
 3. The method of claim2, the third device further determining to transmit during a data unittransmitted in the particular subset of the plurality of service setswhen the transmit power used by the third device is less than theminimum transmit power for the particular subset of the plurality ofservice sets.
 4. The method of claim 3, wherein the transmissionexchanges include (a) a non-high efficiency data unit sent by the firstdevice followed by a high-efficiency data unit sent by the first deviceand an acknowledgment; (b) a Beacon frame sent by the first device,followed by a high-efficiency data unit sent by the first device and anacknowledgement; (c) a request-to-send/clear-to-send exchange before ahigh efficiency data unit; or (d) a short legacy data unit followed byan acknowledgment before a high efficiency data unit.
 5. The method ofclaim 2, further comprising the third device sending, to one or moreassociated client devices, data for the minimum transmit power, withrespect to particular subset of the plurality of service sets, orreceiving from one or more client devices, data or the minimum transmitpower.
 6. The method of claim 1, wherein the clear channel accessparameter is based on a sum of a transmit power used by the first deviceto transmit the second data unit to the second device and a receivesignal strength of the response data unit at the first device.
 7. Themethod of claim 1, wherein determining whether to send comprisesdetermining to send the transmission to the fourth device when the clearchannel access parameter is greater than a sum of the transmit power tobe used by the third device for the transmission to the fourth deviceand the receive signal strength of the response data unit received bythe third device.
 8. An apparatus comprising: a communication interfaceconfigured to enable network communications; a processing device coupledwith the communication interface, and configured to: store a receivesignal strength of a received response data unit transmitted by a firstdevice in response to reception by the first device of a first data unittransmitted by a second device; obtain a clear channel access parameterincluded in a header of a second data unit transmitted by the seconddevice to the first device; detect transmission exchanges in each of aplurality of service sets for use as samples of overlapping service setactivity in a wireless network environment; determine a minimum transmitpower to be used, with respect to a particular subset of the pluralityof service sets, based on the transmission exchanges between devices inthe particular subset of the plurality of service sets; and determinewhether to send a transmission to a third device based on a comparisonof the clear channel access parameter with a sum of the minimum transmitpower to be used for transmission to the third device and the receivesignal strength of the received response data unit.
 9. The apparatus ofclaim 8, wherein the processing device is further configured to: computea maximum transmit power permitted to be used, with respect to theparticular subset of the plurality of service sets, based ontransmission exchanges between devices in the particular subset of theplurality of service sets; compute a first minimum of the maximumtransmit power over a time window spanned by a predetermined number oftransmission exchanges and a second minimum of the maximum of thetransmit power since a most recent time window; update the minimumtransmit power to be used, with respect to the particular subset of theplurality of service sets, based on a minimum of the first minimum andthe second minimum; and store the minimum transmit power with respect tothe particular subset of the plurality of service sets.
 10. Theapparatus of claim 9, wherein the processing device is furtherconfigured to: determine to transmit during a data unit transmitted inthe particular subset of the plurality of service sets when the transmitpower used is less than the minimum transmit power for the particularsubset of the plurality of service sets.
 11. The apparatus of claim 10,wherein the transmission exchanges include (a) a non-high efficiencydata unit sent by the second device followed by a high-efficiency dataunit sent by the second device and an acknowledgment; (b) a Beacon framesent by the second device, followed by a high-efficiency data unit sentby the second device and an acknowledgement; (c) arequest-to-send/clear-to-send exchange before a high efficiency dataunit; or (d) a short legacy data unit followed by an acknowledgmentbefore a high efficiency data unit.
 12. The apparatus of claim 9,wherein the processing device is further configured to: send, to one ormore associated client devices, data for the minimum transmit power,with respect to particular subset of the plurality of service sets, orreceiving from one or more client devices, data or the minimum transmitpower.
 13. The apparatus of claim 8, wherein the clear channel accessparameter is based on a sum of a transmit power used by the seconddevice to transmit the second data unit to the first device and areceive signal strength of the response data unit at the second device.14. The apparatus of claim 8, wherein the processing device is furtherconfigured to: determine to send the transmission to the third devicewhen the clear channel access parameter is greater than a sum of thetransmit power to be used for the transmission to the third device andthe receive signal strength of the response data unit received.
 15. Oneor more non-transitory computer readable storage media encoded withinstructions that, when executed by a processor, cause the processor to:store a receive signal strength of a received response data unittransmitted by a first device in response to reception by the firstdevice of a first data unit transmitted by a second device; obtain aclear channel access parameter included in a header of a second dataunit transmitted by the second device to the first device; detecttransmission exchanges in each of a plurality of service sets for use assamples of overlapping service set activity in a wireless networkenvironment; determine a minimum transmit power to be used, with respectto a particular subset of the plurality of service sets, based on thetransmission exchanges between devices in the particular subset of theplurality of service sets; and determine whether to send a transmissionto a third device based on a comparison of the clear channel accessparameter with a sum of the minimum transmit power to be used fortransmission to the third device and the receive signal strength of thereceived response data unit.
 16. The non-transitory computer readablestorage media of claim 15, wherein the instructions further cause theprocessor to: compute a maximum transmit power permitted to be used,with respect to the particular subset of the plurality of service sets,based on transmission exchanges between devices in the particular subsetof the plurality of service sets; compute a first minimum of the maximumtransmit power over a time window spanned by a predetermined number oftransmission exchanges and a second minimum of the maximum of thetransmit power since a most recent time window; update the minimumtransmit power to be used, with respect to the particular subset of theplurality of service sets, based on a minimum of the first minimum andthe second minimum; and store the minimum transmit power with respect tothe particular subset of the plurality of service sets.
 17. Thenon-transitory computer readable storage media of claim 16, wherein theinstructions further cause the processor to: determine to transmitduring a data unit transmitted in the particular subset of the pluralityof service sets when the transmit power used is less than the minimumtransmit power for the particular subset of the plurality of servicesets.
 18. The non-transitory computer readable storage media of claim17, wherein the transmission exchanges include (a) a non-high efficiencydata unit sent by the second device followed by a high-efficiency dataunit sent by the second device and an acknowledgment; (b) a Beacon framesent by the second device, followed by a high-efficiency data unit sentby the second device and an acknowledgement; (c) arequest-to-send/clear-to-send exchange before a high efficiency dataunit; or (d) a short legacy data unit followed by an acknowledgmentbefore a high efficiency data unit.
 19. The non-transitorycomputer-readable storage media of claim 16, wherein the instructionsfurther cause the processor to: send, to one or more associated clientdevices, data for the minimum transmit power, with respect to particularsubset of the plurality of service sets, or receiving from one or moreclient devices, data or the minimum transmit power.
 20. Thenon-transitory computer-readable storage media of claim 15, wherein theclear channel access parameter is based on a sum of a transmit powerused by the second device to transmit the second data unit to the firstdevice and a receive signal strength of the response data unit at thesecond device.